The present invention pertains to gun fired fin stabilized, discarding sabot projectiles. While proceeding along their trajectory from gun to target, such projectiles experience a reduction in velocity due to the action of aerodynamic drag. Since the terminal effectiveness of such kinetic energy armor piercing ammunition is in the first order a function of the impact velocity at the target, a reduction of the velocity decay during flight to the target is a powerful way to improve their performance, particularly at extended target ranges.
A typical fin stabilized armor piercing projectile with its discarding sabot, for example, is described in U.S. Pat. No. 4,901,646. Since the projectile is subcaliber, which implies that all its cross-sectional dimensions including the span of the fins, are less than the bore diameter of the gun barrel, the sabot is needed to support the projectile during travel in the barrel. Upon exit from the muzzle of the barrel the sabot is discarded automatically and the projectile is free to travel along its trajectory to the target.
A subcaliber fin stabilized long rod projectile is comprised of a cylindrical columnar main body, having an essentially conical nose configuration at front and a fin assembly for aerodynamic stabilization attached to its rear. To achieve the desired performance the projectile body preferably consists of a high density, high strength alloy such as tungsten heavy metal or depleted uranium. Characteristically, the fin assembly consists of four or more fins symmetrically arranged around the main body of the projectile. The subcaliber finned projectile is contained coaxially within the sabot and therefore travels along the axis of the gun barrel during launch. In addition to centering and radially supporting the subcaliber projectile, the sabot transmits the longitudinal acceleration caused by the gas pressure of the burning propellant to the subcaliber projectile. To facilitate this transmission a portion of the main body of the projectile is provided with a series of annular grooves which engage an equivalent mating section within the sabot. As an alternate the annular grooves may be substituted with a length of threads provided on the cylindrical body of the subcaliber projectile and engaging a mating thread on the interior of the aluminum sabot body.
In prior art the length of the grooved or threaded portion extends over a major portion of the cylindrical body of the subcaliber projectile varying in length from 4 to 10 times the diameter of said body, and some instances, over the entire length of the cylindrical body, i.e. from the fin assembly to the shoulder of the projectile nose. While the annular grooves or the threaded portion of the subcaliber projectile is adequate to transfer the launch acceleration from the discarding sabot, its configuration, particularly its length and location, induces adverse effects on the aerodynamic performance during flight to the target resulting in increased velocity decay and correspondingly lower impact velocities at the target. It is an object of this invention to reduce the adverse aerodynamic effects of the structural interface and resultant excessive velocity decay.